Fig. 1. Schematic of SERS spectrum detection of AFP

Fig. 2. Characterization results of AgNPs. (a) Absorption spectrum in ultraviolet and visual band; (b) transmission electron micrograph

Fig. 3. Assembly characterization results of AFP SERS sensor. (a) SEM image of silver nanoparticles assembled on silicon dioxide sheets; (b) Raman mapping of 4-mercapto benzoic acid absorbed on 2D SERS substrate; (c) side-SEM image of two coupled silver nanoparticles on a silica sheet

Fig. 4. Sensitivity detection results of 2D SERS substrates. (a) SERS spectra of 4 MBA with different concentrations; (b) SERS intensity at the peak of 1075 cm^-1 versus the logarithm of concentration of 4 MBA

Fig. 5. AFP test results. (a) ROX SERS spectra with different AFP mass concentrations; (b) linear relationship between logarithm of AFP mass concentration and intensity of ROX SERS spectrum at 1645 cm^-1

Fig. 6. Specificity test results. (a) SERS spectra of AFP specific detection; (b) intensity variation of SERS signal peak of ROX at 1503 cm^-1 after adding equal amount of different proteins